The layer thickness of immiscible liquids is being measured by manual techniques which involve either knowing the layer thickness from the known volume of liquids and the diameter of the container or visually reading the layer thickness using a scale or graduations provided on the container wall. It may be mentioned that the optical techniques based on using optical fibers and lasers for this application are mostly under research and development stage at present.
The conventional techniques are based on human observation and their accuracy shall depend on the person to person while the present technique is based on the principle of Fresnel reflection, which is quite sensitive to changes in refractive index of the medium making contact with the fiber end face. The layer thickness monitoring of immiscible liquids is a very natural and novel application of this technique because, every liquid is identified by its optical parameter which is refractive index. In this technique, the changes in refractive index are read photometrically in term of optical power variations using sensitive photodetectors. This technique based on instrumentation besides being more accurate is also more reliable, efficient and fast as compared to those based on direct human observation. In addition, this technique is more suitable for an industrial application where speed, efficiency and automatic remote monitoring are the highly desirable features.
This technique is useful for remote layer thickness monitoring of immiscible liquids in an industrial process. It is particularly useful for monitoring layer thickness of immiscible liquids in hostile, inflammable, corrosive and electro-magnetically noisy environments as encountered in petrochemical and process control industry.
The novelty aspect of the present invention is the application of the principle of Fresnel reflection in optical fibers that depends on the difference of refractive indices of the fiber core and the surrounding medium. This technique overcomes the above-mentioned problems effectively and provides the added advantage of remote and in-situ monitoring. There is no electrical signal being guided and it is only the light signal which is transmitted through optical fibers and is unaffected by the presence of electrical signals.
A research paper based on this technique for measurement of temperature, contamination and layer thickness of immiscible liquids has been published in Experimental Techniques (USA), 36–38, March/April 2002 printed by the Society for Experimental Mechanics (SEM), Inc., 7 School Street, Bethel, Conn. 06801, (203) 790–6373, www.sem.org.